The present invention relates to a discretionary interconnect and, specifically, to an interconnect which can be programmed or wired through the selective connection and disconnection of the underlying transmission wires at vias selectively placed about the interconnect.
Interconnects, as building blocks for electronic circuitry and microcircuitry, typically receive and support further electrical devices, for example, substrates, i.e., smaller scale interconnects, integrated circuit chips, capacitors, resistors, and so forth, which can be electrically connected to one another to produce larger, more complex electrical structures. The interconnects typically have a sandwich-type structure through which a series of wires extend. The wires connect the electrical devices attached to the interconnect according to a plan specified by the interconnect user.
The interconnects are used in a multiplicity of designs, each requiring unique electrical circuitry. Presently, in a majority of the interconnects, the wiring plan is fixed at an early stage of manufacture. In other words, the manufacturer lays down the interconnect wiring according to a specific, predetermined plan. Such interconnects will be referred to as "design specific". As is readily apparent, design specific interconnects cannot be mass produced, except for high volume applications and are, therefore, time and cost intensive.
There is a need in the interconnect industry for an interconnect design which can be mass produced in an unspecified manner and, thereafter, programmed to produce whatever wiring plan is required by the user. Such interconnects will be referred to as "discretionary interconnects" and the final step of imposing the wiring plan on the interconnect will be referred to as "customization."
Recent efforts in this area have yielded interconnect structures having orthogonal, nonplanar arrays of transmission lines. The lines are generally in the shape of a grid with x-direction lines in one plane and y-direction lines in another plane. These lines are then joined to form the interconnect network. Reference is made to U.S. application Ser. No. 102,172, filed Sept. 29, 1987, to David H. Carey, and Ser. No. 158,172, filed Feb. 19, 1988, to Lawrence N. Smith, for descriptions of discretionary interconnects of this type.
A particular problem incurred by this type of design is the control of characteristic impedance. As a solution to this problem, conductive or ground planes are placed on either side of the x-y wiring structure to achieve a controlled impedance. However, because of the fact that the interconnect must be subsequently accessed to customize the interconnect, i.e., program the wiring network, the ground planes cannot be continuous. As the access area increases, the ability of the ground planes to control impedance diminishes.
U.S. Pat. No. 4,560,962 discloses an interconnect structure which is designed to control impedance; however, the structure is very burdensome. The design is not discretionary, but instead, the via, or points of wiring modification as will be described below, must be custom fabricated to suit each application. The design, therefore, offers limited capability to program the structure to the particular application.
In contrast, U.S. Pat. No. 2,019,625 discloses a discretionary apparatus having a grid of wires buried in a support structure with access points at select areas of wire overlap. However, this apparatus does not have ground planes and is not concerned with controlled impedance. The disclosure relates to the assembly of radio sets (pre-WW II) with a universal wiring pattern. The structure is adequate for that purpose where low to moderate signal frequencies (less than 10 MHz) are involved. In this case, the signal rise time (longer than 30 nanoseconds) is significantly longer than the transit time through the circuit (if 1 foot dimensions prevail, the signal will transit in about 2-3 nanoseconds) and therefore impedance controlled circuitry, such as would be provided by ground planes and microstrip, is not required.
Accordingly, there exists a need for a discretionary interconnect which provides sufficient means for customizing the wiring network, while providing adequate impedance control.